There are multiple surgical techniques for treating a clouding of the lens, which is referred to as a cataract in medicine. The most widespread technique is phacoemulsification, in which a thin hollow needle is introduced into the eye lens and induced to make ultrasonic vibrations. In its immediate surroundings, the vibrating hollow needle emulsifies the lens such that the resulting lens particles can be aspirated through a line by a pump. A flushing fluid (irrigation fluid) is fed during this process, with the aspiration of the lens particles and of the fluid taking place through an aspiration line. When the lens has been completely emulsified and removed, a new artificial lens can be inserted into the empty capsular bag, and so a patient treated in this way can reattain good vision.
During fragmentation of the eye lens by a hollow needle vibrating with ultrasound, it is not possible to avoid a relatively large lens particle reaching the tip of the hollow needle during the surgical procedure such that the needle tip or its aspiration opening becomes clogged. This state is referred to as occlusion. In such a case, a peristaltic pump typically used in the aspiration line builds up a suction pressure which is much stronger in comparison with an occlusion-free operation. In addition, a high energy input for movement of the hollow needle can be effected, so that the lens particle clogging the hollow needle is broken to pieces. Alternatively, a reversal of the direction of movement of the peristaltic pump can also remove the lens particle from the needle tip, and so a normal aspiration of the fluid and of the small lens particles can proceed again. In such a moment, an occlusion is therefore broken up, with the previously present high negative pressure decreasing very rapidly. The resulting suction can lead to not only small lens particles and fluid being drawn to the aspiration line, but also part of the capsular bag coming into contact with the hollow needle. If the capsular bag is punctured, this leads to considerable complications for the patient, which complications must be absolutely avoided. Moreover, during the suction, a large quantity of fluid can be aspirated from the anterior chamber of the eye, and so there is the risk of the eye collapsing. This too can lead to considerable complications for the patient, which complications must be absolutely avoided.
Further systems for steering a fluid are described in United States patent application publication 2015/0164690 A1, WO 93/18802 A1 and United States patent application publication 2015/0297405 A1.